Linear solenoid

Abstract

A linear solenoid has a first magnetic pulling portion for attracting a forward end of a plunger in a forward direction. The linear solenoid further has a second magnetic pulling portion at a rear end of the solenoid. A magnetic path portion is formed at the rear end of the solenoid and composed of a constant overlapping area and a temporal overlapping area. A plunger side-gap portion is formed at a rear end of the plunger so as to face to the overlapping areas in a radial direction. A first radial gap, which is formed between the constant overlapping area and the plunger side-gap portion, is made larger than a second radial gap, which is formed between the temporal overlapping area and the plunger side-gap portion.

1. A linear solenoid comprising:
 a cylindrical solenoid housing made of magnetic material; 
 a cylindrical electromagnetic coil supported in the solenoid housing for generating magnetic force when electric power is supplied thereto; 
 a plunger made of magnetic material and movably inserted into an inside of the coil so that the plunger is movable in its axial direction, the plunger being biased by a biasing means in a backward direction thereof; 
 a first magnetic pulling portion made of magnetic material and formed at a forward end of the solenoid housing for magnetically pulling a forward end of the plunger in a forward direction when the magnetic force is generated at the coil; and 
 a magnetic path portion formed at a rear end of the solenoid housing and surrounding an outer periphery of a rear end portion of the plunger so that magnetic flux passes in a radial direction of the plunger from the rear end portion to the magnetic path portion, 
 wherein a plunger side-gap portion is formed at the rear end portion of the plunger so that the magnetic flux passes in the radial direction of the plunger from the plunger side-gap portion to the magnetic path portion, and 
 a second magnetic pulling portion is formed at the magnetic path portion for magnetically pulling the plunger side-gap portion in the forward direction when the magnetic force is generated at the coil, 
 wherein the magnetic path portion comprises: 
 a constant overlapping area which overlaps with the plunger side-gap portion in the radial direction, when the plunger is in its rear-most position; and 
 a temporal overlapping area which overlaps with the plunger side-gap portion in the radial direction, when the plunger is moved in the forward direction, wherein the temporal overlapping area is increased as the plunger is further moved in the forward direction, 
 wherein a first radial gap is formed in the radial direction between the magnetic path portion of the constant overlapping area and the plunger side-gap portion, 
 wherein a second radial gap is formed in the radial direction between the magnetic path portion of the temporal overlapping area and the plunger side-gap portion, and 
 wherein the first radial gap is made larger than the second radial gap. 
 
     
     
       2. The linear solenoid according to the  claim 1 , wherein
 the plunger side-gap portion is provided at a position, which is out of an axial-length area of a bobbin for the coil in the axial direction, and 
 an outer diameter of the plunger side-gap portion is made to be equal to or larger than a minimum inner diameter of the bobbin. 
 
     
     
       3. The linear solenoid according to the  claim 2 , wherein
 the outer diameter of the plunger side-gap portion is made to be close to a maximum outer diameter of the bobbin. 
 
     
     
       4. The linear solenoid according to the  claim 1 , wherein
 a projected portion is formed at the magnetic path portion of the temporal overlapping area, so that the projected portion faces to the plunger side-gap portion in the axial direction, and 
 the plunger side-gap portion is magnetically pulled by the projected portion, when the magnetic force is generated at the coil. 
 
     
     
       5. The linear solenoid according to the  claim 1 , wherein
 a tapered portion is formed at the magnetic path portion of the temporal overlapping area or at a forward end of the plunger side-gap portion, such that a thickness of the tapered portion in the radial direction is changed in the axial direction. 
 
     
     
       6. The linear solenoid according to the  claim 1 , wherein
 an outer diameter of the forward end of the plunger, which is magnetically pulled by the first magnetic pulling portion, is made to be equal to or larger than a minimum inner diameter of a bobbin for the coil. 
 
     
     
       7. The linear solenoid according to the  claim 1 , wherein
 a sliding member made of non-magnetic material is arranged between an inner peripheral surface of the magnetic path portion and an outer peripheral surface of the plunger side-gap portion, in order to prevent a direct magnetic contact between the magnetic path portion and the plunger side-gap portion. 
 
     
     
       8. The linear solenoid according to the  claim 7 , wherein
 the sliding member is formed as a separate member inserted into an insertion hole formed in the magnetic path portion at the constant overlapping area, or formed as a coating on an inner peripheral surface of the insertion hole. 
 
     
     
       9. The linear solenoid according to the  claim 1 , wherein
 an annular ring member is inserted into an insertion hole formed in the magnetic path portion at the constant overlapping area, and 
 a sliding member made of non-magnetic material is arranged between an inner peripheral surface of the annular ring member and an outer peripheral surface of the plunger side-gap portion, in order to prevent a direct magnetic contact between the magnetic path portion and the plunger side-gap portion. 
 
     
     
       10. The linear solenoid according to the  claim 9 , wherein
 the sliding member is formed as a separate member inserted into the annular ring member or formed as a coating on an inner peripheral surface of the annular ring member.